1. Field of the Invention
The present invention relates to an interface structure for an electronic apparatus. In particular, the present invention relates to an interface structure, for various electronic apparatuses, with small size and high density and designed to facilitate connecting operations.
2. Description of the Related Art
In recent years, an electronic apparatus such as a communication equipment rarely functions by itself and usually has some electrical connections to other external devices. The method of connection includes various electrical and physical interface conditions, and the number of external line connections per unit device has tended to increase considerably.
As an example of the conventional interface structure of an electronic apparatus such as a communication equipment locker, an telephone exchange or a computer, the arrangement which can realize external connections at the back of the apparatus and connections between the shelves is shown in the perspective view of FIG. 8 and the exploded side view of FIG. 9. As shown in these figures, the communication apparatus comprises a locker 1 and one or a plurality of shelves 2 arranged in the locker 1. The shelf 2 is configured to house a plurality of packages 3, and a back board 4 is mounted to the rear of the shelves 2. The back board 4 has connectors 6 mounted thereto, to which connectors 5 of the packages 3 are fitted. Thus, electrical connection between the packages 3 housed in each shelf 3 is established.
Also, the electrical connection between the shelves 2 is established by cables 8 and connectors 7 arranged on the back of the back board 4 connected to the connectors 6.
For electrical connection to external devices, it is possible to use the cables 8 for inter-shelf connection, but the cables 8 are rarely extended to the outside of the apparatus directly as external lines. This is attributable not only to the problem of the electrical characteristics of the cables but also to the problem of the connection strength of the connectors 6 and 7, a limited number of connections and the connection work. For this reason, a terminal board 9 is arranged on the housing of the locker 1, the terminal board 9 having coaxial cable connectors 10 and signal connectors 11 for external line connection which are connected to the connectors 7 on the back board 4 by special conversion cables 12.
Also, in some cases of the recently-employed external line connection, circuits and connectors are prepared in the apparatus in corresponding to characteristic impedances. As an example of a plurality of kind of connection, as shown in FIG. 8, both the coaxial cable connectors 10 and the signal connectors 11 for external line connection are prepared and one of them is selectively used to adapt the impedance difference of the devices to be connected (other equipments). Also, the packages 3 having two types of circuits are provided, which are selectively used by switching.
The number of external line connections required per apparatus is currently increasing to the range from about 100 channels to about 300 channels. In the conventional method in which the required number of connectors are attached to the back board 4 and connected to the external line connectors on the terminal board 9 by the cables, the allowable number of external line connections is limited to at most 100 channels due to the wiring space or the like.
In addition, a radio interference reduction filter 13 and a lightning arrester 14 are often arranged in the external line interface structure, and the filter 13 and the lightning arrester 14 are conventionally arranged in the package 3 having an interface circuit 15, as shown in FIG. 9.
Further, some apparatuses are arranged to carry out a standby switching operation for failures. To this end, a standby package is arranged in the shelf 2, and the input/output line is switched between the standby package and the operating package in which a failure occurs. A theoretical block diagram with a simplified conventional configuration is schematically shown in FIG. 10.
FIG. 10 shows an 8-to-1 standby switching configuration. When one of packages #0 to #7 develops a failure, the input/output line is switched to the package #8. Realization of this function requires a switching control package 16 capable of switching any lines of packages #0 to #7. This switching control package 16 is arranged in the shelf 2.
The above-mentioned conventional external line connection arrangement includes a measure for meeting the requirements for a plurality of kinds of connections and for the increased number of connections. This conventional arrangement has the following problems: (1) As seen in FIG. 11 showing the rear view of the locker and FIG. 12 showing the side view of the locker, 100 or more external lines may be sometimes required for each shelf 2, resulting not only in an increased cost of equipment and material but in an increased number of wiring operation steps due to the variety of connection forms. (2) In the case of (1) above, the cables from the back board 4 are laid within the locker 1 and connected to the external line connectors 10, 11 on the terminal board 9, and there are a plurality of types of connectors so it is impossible to accommodate more than 100 cables. (3) The radio interference reduction filter 13 is mounted to the package 3, and the noise on the special external line cable 12 is conveyed to the outside, bypassing the filter 13. As a result, there is a possibility that external portions relative to the apparatus are adversely affected. (4) An impedance-switching circuit is required on the package 3, thereby deteriorating the efficiency with which the packages 3 are arranged.
Further, in the circuit to carry out the standby package switching control for failures the switching control package 16 is necessary and the wiring is very difficult since the lines are extended to the switching control package 16 with the increased number of cables on the back board 4, shown in the block diagram of FIG. 10.